1. Field of the Invention
The present invention relates to an ink mixing device, and an ink manufacturing apparatus. In addition, the present invention relates to a method for washing the ink manufacturing apparatus. Further the present invention relates to an ink, and an ink cartridge containing the inkjet ink. Furthermore, the present invention relates to an image forming method and apparatus using the ink, and an print image produced by the image forming method and apparatus.
2. Discussion of the Background
As the inks for use in inkjet printing, fountain pens, felt pens, ink pads and the like, aqueous inks which are prepared by mixing a water-soluble dye or a pigment dispersion with water, a water-soluble organic solvent, a surfactant and the like materials have been typically used. In recent years, large item small scale production is performed on such inks using a mixing apparatus, and therefore a need exists for a mixing apparatus which can efficiently mix such materials as mentioned above in a short period of time. In addition, it is preferable for the mixing apparatus to include bubbles and foreign materials in the products in an amount as little as possible so that the resultant inks have good qualities.
Conventionally, mixing devices having an agitator such as agitating blades have been typically used. However, such mixing devices have drawbacks such that mixing has to be performed for a long time; and when the mixing time is relatively short, the ink constituents are not uniformly dispersed or solid components of the constituents remain in the resultant inks without being dissolved or dispersed therein.
In addition, it is necessary for the mixing devices that the agitator needs to be dipped into the ink constituents in a mixing vessel, i.e., the volume of the ink constituents needs to be at least half the volume of the mixing vessel. Therefore, a small quantity of ink cannot be produced by such mixing devices. Further, a number of bubbles are included in the resultant inks, and thereby problems in that the bubbles present on the surface of the inks dry, resulting in increase of the solid content of the inks or inclusion of dried inks in the inks; and when a pigment is used as a colorant, the dispersed inks aggregate due to the bubbles formed therein tend to occur. Thus, inks having good qualities cannot be produced by such mixing devices.
In addition, such mixing devices have another drawback in that when the mixing devices are washed after production of an ink, it takes a long time to wash the mixing devices because their agitators have a complex shape and therefore should be pulled up to wash the inside of the mixing vessel and the agitators. Even when a small amount of ink remains in a mixing vessel, the ink deteriorates the reliability of the ink which is prepared thereafter. Therefore it is necessary to clean the mixing devices so that the resultant ink has desired qualities.
In attempting to solve the above-mentioned problem, various mixers which perform agitation utilizing flow of the liquid to be agitated have been proposed. FIG. 4 is a schematic view illustrating the cross section of a mixing device utilizing flow of liquid to be agitated (i.e., a jet agitating mixer), which is disclosed in page 427 of Chemical Engineering Handbook. In FIG. 4, a liquid L to be agitated is injected into a vessel 10 from an injection opening 13 in a horizontal direction. He liquid L is agitated and flows in directions indicated by arrows. The liquid L is sucked from a discharge nozzle 11 by a pump P to pass through a tube 12 and is injected again into the mixing vessel 10.
In addition, another mixer utilizing flow of the liquid to be agitated is disclosed in published unexamined Japanese Patent Application No. 63-7828. The cross section of the mixer is illustrated in FIGS. 5A and 5B. In FIGS. 5A and 5B, numerals 21, 22, 23, 24, 25 and 26 denote a mixing vessel, injection/discharge nozzles, a pipe, a discharge opening, a pump and a valve. The liquid is mixed while injected into the mixing vessel 21 or discharged therefrom through the injection/discharge nozzles 22 by the pump 25 to be swirled in the mixing vessel 21.
However, the mixers disclosed in Chemical Engineering Handbook and JP-A 63-7828 have an insufficient mixing efficiency because the liquid located in the bottom of the vessels hardly moves.
FIG. 6 is a view illustrating the cross section of another mixer, which is disclosed in published examined Japanese Patent Application No. 63-33897. Referring to FIG. 6, the mixer has a mixing vessel 31 which has a cylindrical portion 31a and a lower conical portion 31b. The liquid to be mixed is extracted from the mixing vessel 31 through a pipe 33 and injected into the mixing vessel 31 from a first opening 34. In addition, the liquid is also injected into the mixing vessel 31 from a second opening 35 provided on a bottom portion of the conical portion 31b. Further, the liquid is also extracted from the mixing vessel 31 through pipes 36a and 36b and injected into the mixing vessel 31 from nozzles 37a and 37b provided on middle portions of the conical portion 31b. Numeral 32 denotes a pipe through which the liquid is circulated and injected into the mixing vessel 31 and pumps. Character P denotes a pump.
However, this mixer has the following drawbacks:    (1) since a number of openings, pipes and pumps are provided, it is hard to avoid contamination of ink; and    (2) since the second opening is provided so as to face upward, the liquid tends to blow out of the liquid surface if the volume of the liquid is small.
Therefore, the mixer is not suitable for large item small scale production.
FIG. 7 is a view illustrating the cross section of another mixer, which is disclosed in published unexamined Japanese Patent Application No. 2000-60514. Referring to FIG. 7, the mixer has a mixing vessel 40 having a cylindrical or prism form on which injection openings 43 and a discharge opening 44 are provided. In addition, a flow controlling plate 45 which has a predetermined width and which projects in the mixing vessel 40 while slanting at a predetermined angle a is provided on an upper portion of the mixing vessel 40. However, the mixer has the following drawbacks:    (1) the mixer is not suitable for large item small scale production;    (2) bubbles are formed in the liquid; and    (3) it is difficult to wash the flow controlling plate, and therefore it is hard to avoid contamination of ink.
FIG. 8 is a view illustrating the cross section of another mixer, which is disclosed in published unexamined Japanese Patent Application No. 2002-113342. Referring to FIG. 8, the mixer has a mixing vessel 73 and an agitator 74 configured to agitate the liquid to be mixed. The agitator 74 is provided at a lower center position of the mixing vessel 73 and has the following members:    (1) a first liquid guiding pipe 72a configured to blow out the liquid upwardly in the mixing vessel 73;    (2) a swirl flow forming member 75 which is provided in the mixing vessel 73 and which collides with the blown-out liquid to cause the liquid in the mixing vessel 73 to swirl in directions indicated by arrows;    (3) a second liquid guiding pipe 72b having an opening at a bottom portion of the mixing vessel 73 and configured to discharge the liquid from the mixing vessel 73; and    (4) a pump 71 configured to transport the liquid from the second liquid guiding pipe 72b to the first liquid guiding pipe 72a through valves V1 and V5 and form a jet stream of the liquid.
However, the mixer has drawbacks in that a solid component and a gel material tend to remain at the bottom portion of the mixing vessel 73, i.e., the agitating efficiency of the mixer is not satisfactory; and the mixer is not suitable for large item small scale production because the agitator extends in the vertical direction.
Because of these reasons, a need exists for a mixing device which is suitable for large item small scale production and which can efficiently mix an ink in a short period of time without causing problems such that a large volume of babbles are included in the resultant ink and the resultant ink is contaminated with another ink.